Since various items of data are required for controlling motor vehicles, it has been proposed to provide a sensor on a hub unit comprising a wheel-side raceway member to which a wheel is to be attached, a body-side raceway member to be fixed to the vehicle body, and two rows of rolling bodies arranged between the two raceway members.
For example, Patent Literature 1 (the publication of JP-A No. 3-209016) discloses a sensor-equipped hub unit wherein an annular support member is attached to the inner end face of a body-side raceway member and provided with a strain sensor.
Further Patent Literature 2 (the publication of JP-A No. 1-206113) discloses a sensor-equipped antifriction bearing unit which comprises an antifriction bearing having a fixed-side raceway member, a rotation-side raceway member and rolling bodies, and a load- and temperature-measuring strain gauge attached to the outer side of an outer ring serving as the fixed-side raceway member of the antifriction bearing.
In recent years, the control means in use for motor vehicles include drive force control means not permitting spinning of the drive wheels when the vehicle is started or accelerated, and braking force control means for suppressing lateral skidding for cornering, in addition to the ABS control means (antilock brake system). To ensure more accurate control, it has become important to detect data which is usable effectively for these modes of control.
In view of the above situation, the present inventor has conceived the idea of improving the control of vehicles by accurately measuring the ground contact load acting on the tire.
However, since the hub unit of Patent Literature 1 having a sensor is adapted to measure the strain of the annular support member, the ground contact load determined from the strain involves a great error, so that the hub unit has the problem that the ground contact load can not be obtained with high accuracy from the measurement of the strain sensor. Additionally, a rotation sensor is required for measuring the speed of rotation, and a displacement sensor is necessary for measuring axial displacement.
The antifriction bearing unit of Patent Literature 2 has the advantage that both load and temperature can be measured by a single sensor (strain sensor), whereas the force to be exerted by the rolling bodies on the raceway member involves great measuring errors, so that the unit has the problem that the force acting on the raceway member can not be obtained from the measurement of the strain gauge with high accuracy.
An object of the present invention is to provide a hub unit having a sensor and adapted to measure ground contact loads with high accuracy and to detect the rotation of the wheel.
Another object of the invention is to provide an antifriction bearing unit having a sensor and adapted to accurately measure the force acting on the raceway member of a bearing and to detect rotation.